The present invention relates to a radiation curable hot melt inkjet ink, comprising a carrier composition that comprises one or more radiation curable compounds and an agent that is able to reversibly gel the carrier composition, which agent is soluble in the carrier composition at the jetting temperature of the ink and creates the gelled carrier at a temperature below the jetting temperature. The present invention also pertains to a method of printing a substrate with such an ink.
Such an ink is known from European patent EP 1,090.079. The inks disclosed in this patent are thixotropic pastes, wherein the thixotropic properties are provided for by adding a thickener to the carrier composition that thermally, reversibly gels this composition. In the gelled state, an elastic network of the thickener is formed in the liquid carrier composition, the interstices of the network being filled with the carrier composition. In this way, at ambient conditions, the ink is a pasty gel which prevents inter droplet smear (also called “colour bleed”) of ink droplets printed next to each other on a substrate. By heating the gel, the viscosity can be decreased to become sufficiently low for jetting purposes, typically lower than 20 mPa·s. By heating the gel, the gel network will eventually break down, for example because the gel agent dissolves in the carrier composition. Since the inkjet ink is a gel at ambient conditions and becomes liquid by increasing the temperature, this ink can be regarded as a hot melt ink. Whereas the known inks provide a solution to the problem of inter droplet smear, the applicant has recognized that these inks often immediately set on the surface of the recording medium without sufficiently entering this medium, even if highly porous media such as plain paper are being used. This results, i.e., in the effect that the jetted ink droplets actually protrude from the surface of the recording medium, thereby providing a matte appearance instead of a glossy appearance.